Nickel-chromium alloys



3,166,411 NlCKEL-CHROMIUM ALLOYS Reginald Massey Cook, Birmingham, and John Henry Gittns, Wrea Green, near Preston, England, a'ssignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 21, 1962, Ser. No. 181,437

Claims priority, application Great Britain Oct. 21, 1958 4 Claims. (Cl. 75-171) The present invention relates to nickel alloys for use at high temperatures and, more particularly, .to agehardenable nickel-chromium -cobalt alloys containing molybdenum, aluminum and titanium, and lesser but effective amounts of zirconium, boron and carbon.

It is well known that alloys from which articles and parts are made, e.g., gas turbine blades, which are sub- .United States Patent jected to prolonged stress at high temperatures must not only possess resistance to corrosion at high temperatures and good general mechanical properties, but also by their nature must possess resistance to creep. The alloys used for this purpose are of the kind in which the principal constituent is nickel or nickel plus cobalt and which also contain chromium, aluminum and titanium, these last two elements forming a precipitable phase with some of the nickel. Generally, the alloys also contain carbon, as it is known that these alloys can also form carbide phases which can play an important part in controlling the properties of the alloys. The precise composition of the alloy varies with the conditions under which it is to be used and the properties required under these conditions.

The life-to-rupture of the alloys under given conditions of stress and temperature varies with the composition, and it is frequently found that there is an optimum composition at which a maximum life isobtained under a given set of conditions.

Hitherto, the alloys have commonly been prepared by' melting in air. It is known that in certain cases their high temperature properties can be improved by melting in the absence of air, i.e., in a vacuum furnace. By this means only a moderate improvement in the life-to-rupture of an alloy of a given composition is obtained. Although many attempts were made to provide an alloy having greatly enhanced high temperature characteristics, none, as far as We are aware, was entirely successful when carried into practice commercially on an industrial scale.

it has now been discovered that by employing specially controlled amounts of aluminum and titanium which form a'precipitable phase with some of the nickel in combination in a nickel-chromium-cobalt-containing alloy base, vacuum treating, and/or vacuum melting and vacuum treating the alloy, an alloy is obtained having superior high temperature characteristics in the wrought condition.

It is an object of the present invention to provide novel alloys for high temperature applications.

Another object of the invention is to provide novel alloys having improved properties and characteristics at elevated temperatures.

The invention also contemplates providing novel agehardenable alloys.

It is a further object of the invention to provide a method for producing novel alloys having superior high temperature characteristics.

3,165,411 Patented Jan. 19, 1965 Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates vacuum treated and/ or vacuum melted and vacuum treated, i.e., at a pressure below microns of mercury, nickel alloys for use in the wrought form containing, by weight, about 10% to about 18% chromium, about 3% to about 9% molybdenum, about 15% to about 25% cobalt, at least about 4.5% aluminum, at least about 1.1% titanium, with the proviso that the ratio of aluminum to titanium is between about 3 and about 4.5, and advantageously about 3.5 to 1, about 0.05% to about 0.3% zirconium, about 0.001% to about 0.01% boron, together with carbon in amounts from about 0.1% to about 0.3%, the balance of the alloy, apart from the usual impurities and residual deoxidants, being nickel. The sum of the aluminum plus titanium content is related to the chromium content such that the percentages of the aluminum plus titanium content lies between about A (42 minus percent chromium) and about A (48 minus percent chromium) and advantageously is between about A. (42 minus percent chromium) and about A (46 minus percent chromium), e.g., about A (45 minus percent chromium).

The alloys according to this invention contain chromium, molybdenum, cobalt and small amounts of carbon, boron and zirconium which play an important part in controlling the properties of the alloys. For example, the alloy should contain chromium in the range of about 10% to about 18%, by weight, since the effect of chromium is to provide good resistance to high temperature oxidation and corrosion, whilst giving some creep resistance also. Advantageously, the chromium content is about 11% to about 15% by weight for maximum high temperature characteristics. Molybdenum should be present in the alloy in the range of about 3% to about 9% since it has the effect of improving the stress-rupture life at all levels of the summation of titanium and aluminum. Cobalt in the range from about 15 to about 25%, by weight, is necessary to the alloy as it has the effect of improving the ductility in creep and thereby prolonging the stressrupture life of the alloy. Carbon in the range of 0.1% to 0.3% by weight of the alloy is necessary to the invention. After heat treatment it appears as carbides which have a beneficial effect upon ductility in creep. Zirconium should be present in the alloy in amounts from about 0.05 to about 0.30%. The eifect of the zirconium is to increase the stress-rupture life over a wide range of the titanium plus aluminum contents. Boron is added to the alloy in the range from about 0.001% to about 0.01%. Boron has the advantage of increasing stress-rupture life by diminishing the minimum creep rate.

Iron may be present in amounts up to about 1% by weight of the alloy as well as other impurities and residual deoxidants such as silicon, manganese, calcium, magnesium and copper. Although the effect of these elements is generally to reduce the stress-rupture life of vacuum-melted alloys, their presence may be unavoidable if certain types of scrap are included in the furnace charge.

In carrying the invention into practice, advantageous results are obtained when the bath of molten metal is treated under vacuum by holding the bath under a pressure of not more than 100 microns of mercury and at a temperature of 1400 C. to 1600 C. before casting. The holding period is at least minutes and is advantageously at least minutes. The holding period may be as long as 90 minutes. In general, the longer the period under vacuum, the better the stress-rupture properties of the alloy.

The exact period required for any given melt depends to some extent upon the purity of the ingredients of the melt, a longer period being required for less pure ingredients. However, this is not the only factor involved, as substantial benefits are obtained even when metals of the highest available purity are used to produce the alloys. While the pressure used may be as high as 100 microns of mercury, advantageously lower pressures, for example, 5 microns or less or even pressures of the order of 1 micron of mercury, are used.

The vacuum treatment is advantageously carried out on vacuum-melted alloy. However, the invention also includes alloys which have been melted in air and then held under vacuum as hereinbefore described. Once the alloys have been vacuum melted or treated in the molten state under vacuum or both, it makes little difference to their properties whether they are cast in vacuum or in air.

When the alloys are vacuum melted or treated in the molten state under vacuum, the optimum composition of the alloys is diiferent than when the alloys are melted in air. Hitherto, it has been assumed that the improvement in life-to-rupture associated with vacuum melting was due to the removal of dissolved gases from the molten metal during the melting process and the consequent elimination of undesirable oxide and nitride inclusions which are known to exert a weakening effect in metals and alloys, and it was totally unexpected that the relative performance of alloys of different compositions would be effected.

For the purpose of giving those skilled in the art a better understanding of the invention, a number of alloys are set forth in Table I.

Table I Serie Per- Per- Per- Al: Ti Per- Per- Perler- No. cent cent cent Ratio cent cent cent cent 01' 00 Mo Zr B 0 Ni 1 11 20 i 5 3.5:1 0.05 0.003 0.22 Bal. 2 5 3. 5:1 0.05 0.003 0. l5 Bal.

Each series included alloys having dillerent total alumiof 7 tons per square inch (t.s.i'.), exhibiting the charac- 10% by Weight.

Ingots from the No. 1 and No. 2 series were prepared in two ways. Firstly, each of the alloys was air melted and cast. Secondly, each of the alloys was vacuum melted under a pressure of less than 1 micron of mercury. After vacuum melting, each of the alloys was held at a temperature of 1500 C. under. a vacuum of less than 5 microns of mercury for ten minutes and then was'cast into ingots. Thereafter, the ingots were hot worked to produce bar. The bar produced from alloys of series No. 1 was heat treated as follows: heat to about 1200 C. for 1 /2 hours; air-cool to room temperature; then reheat to 850 C. and hold at that temperature for 16 hours; and air-cool to room temperature. The .bar from alloys of series No. 2 was similarly heat treated except that the heating was conducted at a temperature of 1050 C. for 16 hours. It is to be noted that the reheat temperature lies between about 800 C. and about 1100 C. Furthermore, the reheat temperature is so coordinated with the chromium content that when the chromium content is be.- tween about 10% and about 15% the reheat temperature in degrees centigrade is about 1050 minus (15 minus percent chromium). When the chromium content is in the range of 15% to about 18% by weight of the alloy, the reheat temperature is in the range of about 1050 C. to about 11001 C. and does not exceed 1100 C. at the highest chromium content, i.e., 18%. The heat-treated bars were stress-rupture tested at 940 C. and at a stress teristics set forth in Table Ill.

Table II Air Melted Vacuum Melted and Vacuum Treated Al+'li, I

Series Alloy Percent Minimum Minimum Rupture Secondary Rupture Secondary Lilo Creep Rate Life Creep Rate (Hours) (Percent (Hours) (Percent Hour) 7 Hour) 1 A 6 26 B 6. 5 79 0. 043 94 0. 037 O 7 0.015 0. 012

2 A 5 25 31 B 6 97 0.015 0.013 O 7 94 0.029 261 0.012 D '7. 5 312 0.007 E 8 11 243 0. 018 'F 9 50 Thus, from Table II it is to be noted that at the lower aluminum plus titanium contents vacuum melting and vacuum treating provided only slight increases in the rupture life of the alloys, and that the lives of the airmelted alloys were not much improved by increasing the aluminum plus titanium content above about 7% for the alloys of series No. 1 and-about 6% for the alloys of series No. 2. However, 'by varying the total content of aluminum plus titanium while maintaining the same ratio of aluminum to titanium in accordance with the present invention, the greatest lives of the vacuum-melted and vacuum-treated alloys were found to occur at substantially higher aluminum plus titanium contents. The markedly superior high temperature characteristics that are obtained in the alloys having the optimum aluminum plus titanium contents are exemplified by alloy E of series No. 1 and alloy D of series No. 2 in the vacuum-melted and vacuum-treated condition.

In the vacuum-treated alloys of this invention, improvements in stress-rupture life can be effected by modification of the zirconium content. Thus, when alloys such as those illustrated by alloys of series No. 1 contain up to 0.3% zirconium, e.g., 0.2% zirconium, the life-to-rupture when tested at 940 C. and 7 t.s.i. is nearly 500 hours. In the case of an alloy containing 15% chromium, as illustrated by the alloys of series No. 2, the optimum Zirconium content is less, i.e., between about 0.05% and 0.1% zirconium. Ordinarily, in the alloys of this invention, it is found that raising the chromium content whilst maintaining the optimum total aluminum plus titanium content, causes a decrease in the optimum zirconium content.

Alloys having compositions within the invention and particularly those having an aluminum plus titanium content within the advantageous range have excellent properties at even higher temperatures than 940 C. For example, alloys within the invention having lives to rupture of 200 hours at 940 C. and 7 tons per square inch have rupture lives in excess of 100 hours at 960 C. under the same stress.

The alloys of the present invention are particularly adapted to be employed as components in gas turbines and other articles which are subjected to stress at elevated temperatures.

The present application is a continuation-in-part of our copending patent application Serial No. 846,552, filed October 15, 1959, now abandoned.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of'the invention and appended claims.

We claim: 1 1. An alloy capable of being age-hardened consisting b 3. An age-hardenable alloy consisting essentially of about 15% chromium, about 3% to about 9%n1olyb- .denum,"about 15% to about 25 cobalt, aluminum and essentially of about to about 18% Chromium, about 3% to about 9% molybdenum, about %'to about cobalt, at least about 4.5% aluminum, at least about 1.1%

titanium, with the proviso that the ratio of aluminum content to titanium content isbetween about 3 to land about 4.5 to 1, about 0.05% to about 0.3% zirconium,

about 0.001% to about 0.01% boron, together with carbon in amounts from about 0. l0% toabout 0.30%, the 4 balance essentially nickel, said alloy having the amounts of aluminum plus titanium and chromium so interrelated that the alloy contains the percentage of aluminum plus titanium in total amountsrelated to the chromium contents such that the aluminum pius titanium content of the alloy is about /4 times the quantity (42 minus percent chromium) to about 4 times the quantity (48 minus percent chromium) with the ratio of aluminum to titanium being about3z1 to about 4.5:1, about 0.05% to about 0.30% zirconium, about 0.001% to about 0.01%

. boron, about 0.10% to about 0.30% carbon and the balance essentially nickel, said alloy when vacuum treated being characterized by having a life-to-rupture in excess fof 200 hours at a temperature of 940 C. and at a stress titanium in amounts equal to about A times the quantity (42 minus percent chromium): to about A times the quantity (46 minus percent chromium), said alloy when vacuum treated being characterized by having a life-torupture in excess of 200 hours at a temperature of 940 C. and at astre'ssof 7' tons per square inch. p ssentially of 2. An age-hardenable alloy consisting about 11% to about 15% chromium, about 3% to about 9% molybdenum, about 15% to about.25% cobalt, aluof 7 tons per square inch,

4. An age -hardenable alloy consisting essentially of about 15% chromium, about 5% molybdenum, about 1; 20% cobalt, aluminum plus titanium in a total amount minum and titanium in total amounts related to'the chromium content such that the aluminunrplus titaniurn is about 8% when thechromiumcontent is about 11% and such that the aluminum plus titaniumfis about-7% to about i i 8% when the chromium contentis'about 15% with the ratio of aluminum to titaniurnbeing between about 3:1 and about 4.5 :1, about 0.001% to' about O. 0l% -boron, about 0.05 to about 0.30% zirconium, about 0.10% to about 0.30% carbon and the balance essentially nickel, said alloy when vacuum treated being characterizedby having a life-to-rupture in excess of 200 hours at attem- 'perature of 940 C a'nd:at astress of 7 tons .per square inch. e

between about 7% and 8% with the ratio of aluminum to titanium being between about 3:1;and 4.5 :1, about 0.05 to about 0.30% zirconium, about 0.001% to about 0.0 1% boron, about 0.10% to about 0.30% carbon and the balance essentially nickel, said alloy when vacuum treated being characterized by" having a life-to-rupture in excess of 200 hours at a temperature of 940 C. and

v at a stress of 7 tons per square inch.

' V Refereiicesfiited in the'file of this patent UNITED STAIES PATENTS 1 548,778 v Canada Nov. 12, 1957 

1. AN ALLOY CAPABLE OF BEING AGE-HARDENED CONSISTING ESSENTIALLY OF ABOUT 10% TO ABOUT 18% CHROMIUM, ABOUT 3% TO ABOUT 9% MOLYBDENUM, ABOUT 15% TO ABOUT 25% COBALT, AT LEAST ABOUT 4.5% ALUMINUM, AT LEAST ABOUT 1.1% TITANIUM, WITH THE PROVISO THAT THE RATIO OF ALUMINUM CONTENT TO TITANIUM CONTENT IS BETWEEN ABOUT 3 TO 1 AND ABOUT 4.5 TO 1, ABOUT 0.05% TO ABOUT 0.3% ZIRCONIUM, ABOUT 0.001% TO ABOUT 0.01% BORON, TOGETHER WITH CARBON IN AMOUNTS FROM ABOUT 0.10% TO ABOUT 0.30%, THE BALANCE ESSENTIALLY NICKEL, SAID ALLOY HAVING THE AMOUNTS OF ALUMINUM PLUS TITANIUM AND CHROMIUM SO INTERRELATED THAT THE ALLOY CONTAINS THE PERCENTAGE OF ALUMINUM PLUS TITANIUM IN AMOUNTS EQUAL TO ABOUT 1/4 TIMES THE QUANTITY (42 MINUS PERCENT CHROMIUM) TO ABOUT 1/4 TIMES THE QUANTITY (46 MINUS PERCENT CHROMIUM), SAID ALLOY WHEN VACUUM TREATED BEING CHARACTERIZED BY HAVING A LIFE-TORUPTURE IN EXCESS OF 200 HOURS AT A TEMPERATURE OF 940* C. AND AT A STRESS OF 7 TONS PER SQUARE INCH. 